Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $247.44   10.716%   $273.9557   $273.96   $273.95   $274.00  
  Purchase #2 $43.35   6.704%   $46.2562   $46.26   $46.25   $46.30  
  Purchase #3 $242.43   8.105%   $262.079   $262.08   $262.10   $262.10  
  Purchase #4 $229.64   13.592%   $260.8527   $260.85   $260.85   $260.90  
  Purchase #5 $236.74   3.193%   $244.2991   $244.30   $244.30   $244.30  
  Purchase #6 $126.50   6.665%   $134.9312   $134.93   $134.95   $134.90  
  Purchase #7 $153.45   5.790%   $162.3348   $162.33   $162.35   $162.30  
  7 purchase totals = $1,279.55       $1,384.7087   $1,384.71   $1,384.75   $1,384.80